Retaining blocks and modular plug inserts for electrical connectors are known in the prior art. In the known solutions, contacts are introduced along a plug-in direction of a fitted plug into the retaining block and fixed in the retaining block with, for example, a latching hook. Each contact can have its own latching hook. The modular plug insert, in which the cables are fastened with the latching hook, must further be fastened in the plug housing, thereby requiring a second locking means. This locking can be carried out by further latching hooks, by a screwed-in locking, or by extrusion-coating of the contacts. Fastening the cables in the retaining block or plug insert increases the difficulty in mounting the plug insert, and further, increases the required size of a mating face of the plug insert.